Composting is the biological conversion of organic wastes, such as vegetable refuses, woodchips, leave litters or food wastes, into valuable products, such as fertilizers, substrates for growing mushroom, or biogas (methane) for use as energy sources. In comparison with chemical fertilizers, organic fertilizers are less expensive and have many agricultural advantages. For instances, soil modified with composts or organic fertilizers showed improvement of total porosity, increase of water stable aggregates (Nnabude, P. C., and Mbagwu, J. S., 2001, Bioresour. Technol., 76:265-272) and accumulation of metals in soil (Guerrero, et al., 2001, Bioresour. Technol., 76: 221-227; and Zinati, et al., 2001, J. Environ. Sci. Health B. 36: 229-243). Crop yield was enhanced and the growth period thereof was shortened (Ferrer, et al., 2001, Bioresour. Technol. 76: 39-44; Nnabude and Mbagwu, supra; and Guerrero, et al., supra). Termine, et al. found that leeks and turnips grown under organic fertilizations had less nitrate contents than those grown under inorganic fertilizations (Termine, et al., 1987, Plants Foods Hum. Nutr. 37:321-332).
Moreover, compost-modified soil could suppress occurrence of diseases on growing plants (Wuest, P. J., and Forer, L. B., 1975, Mycopathologia 55: 9-12; Kannangara, et al., 2000, Can. J. Microbiol. 46: 1021-1028). Therefore, the amounts of pesticides and fungicides used can be reduced or eliminated. In addition, since soil organisms can be killed by these pesticides and fungicides, it is considered that composts or organic fertilizers are environmentally safe and capable of retaining soil fertility. In fact, the soil modification with compost has been demonstrated as an effective method in remediation of contaminated soil (Vouillamoz, J., and Mike, M. W., 2001, Water Sci. Technol. 43: 291-295; Semple, et al., 2001, Environ. Pollut. 112: 269-283).
During composting, the active component mediating the biodegradation and conversion is the resident microbial community. As a composing process proceeds, the microbial community changes. For instance, some microbes were enriched and some were eliminated during the process (Peters, et al., 2000, Appl. Environ. Microbiol. 66: 930-936).
For many households or companies, plant leaves constitute the main portion of the starting materials for making organic fertilizers or composting. Crucifer plants are the most important vegetables worldwide, including Brassica chinensis, broccoli, cabbage, cauliflower, Brussels sprouts, Chinese cabbage, kale, radish, turnip and mustard. Leaves of the crucifers are either edible or discarded. Xanthomonas campestris pv. campstris is a bacterial pathogen of crucifer plants. It infects the leaves of the plants through natural openings (stomata and hydathodes) or wounds due to insect bites, resulting a black-rot disease of the plants (Williams, P. H., 1980, Plant Dis. 64: 736-742).
In addition, a compost-based biofilter for degradation of organic compounds have also been successfully developed (Lee, et al., 1999, J. Air Waste Manag. Assoc. 49: 1068-1074; Juteau, et al., 1999, Appl. Microbiol. Biotechnol. 52: 863-868). The biofilter is beneficial for the industry and the environment, such as bioremediation of hazardous waste sites, biofiltration of industrial water or air and forming a biobarrier to protect soil and ground water from contamination.
Our earlier studies showed that a spontaneous avirulent mutant of X. campestris pv. campstris strain 11(Xc11), which was called Xc11A, was likely resulted from transposition of a specific copy of insertion sequence IS1478a (Chen, et al., 1999, J. Bacteriol., 181: 1220-1228) located in the genome of Xc11 to a position of 352 bp downstream (Hsiau, S. L., 1996, thesis, National Chung Hsing University). It is desired to isolate the black rot gene from Xc11 or the related strains and obtain a gene product useful in degradation of organic plant materials in a fast, efficient, simplified, controllable and environmentally safe manner.